This invention relates to leak testing of pipe sections by means of a pressurized test gas, and more particularly to a method and apparatus for testing for minute leakage at a test section and including an enclosure device for confining any test gas that leaks through the test section.
The testing of fluid conduits for leak tightness is a common requirement, especially in the oil and gas well field. In the oil field, the testing of pipe joints is especially important to prevent leakage of the gas or oil out of the pipe and loss into the surrounding ground around the bore hole. Typically in such applications, a hole is drilled in the earth, and as the depth of the hole increases a well casing, in the form of a pipe, is inserted behind the drill to define the well bore and to permit the introduction and withdrawal of drilling fluids, as well as the withdrawal of drilling debris. Several sections of such a well casing when connected together are referred to as a well string, and the string is defined by a series of interconnected pipe sections, the interconnections most often being accomplished by means of an internally threaded union which engages corresponding external threads at each of the opposed ends of the pipe sections to be joined.
Testing of such pipe joints for leak tightness has most often been accomplished by subjecting the pipe joint to high internal fluid pressures. A suitable pipe testing tool is introduced into the interior of the pipe, the tool being such that it includes spaced resilient packing glands which are radially extendable against the interior surface of the pipe on opposite sides of the area to be tested to thereby define an annular space into which a pressurized liquid, such as water, can be introduced. An example of a highly preferred pipe testing tool is shown in U.S. Pat. No. 4,548,069, issued Oct. 22, 1985, entitled "Pipe Testing Tool", and owned by the same assignee, the disclosure of which application is incorporated herein by reference. Alternate tools are shown in U.S. Pat. No. 3,899,920. Any leakage of water through the joint can then be visually detected, whereupon suitable corrective action can be taken.
In addition to the use of pressurized water, it has become accepted practice when testing pipe for deeper wells to employ pressurized gas or gases, especially nitrogen gas, to check pipe joints for leak tightness. This is particularly true for testing leak tightness at pressures in excess of about 10,000 psi. A similar pipe testing tool is employed to introduce the pressurized gas to the interior of the pipe (see, for example, the aforesaid U.S. Pat. No. 4,548,069, and a liquid film is applied to the outside surfaces of the joint in order to visually observe leaking gas bubbles.
Alternatively, when pressurized nitrogen gas has been used in the testing tool, a cup-like member was positioned around and under the exterior of the joint section to be tested, and tightly engaged the section of pipe immediately below the test section to define an external annular chamber open at the top and closed at the bottom. Water was placed in the annular chamber, and a leak site manifested itself by the appearance of nitrogen bubbles rising in the surrounding water, which can be visually detected. An example of such a "bubble bucket" is shown in U.S. Pat. No. 3,385,103, issued May 28, 1968, to John F. Wilkerson.
Nitrogen gas has limitations with respect to the size of leak sites which can be detected and the speed with which nitrogen gas can disclose the existence of very small leak passages. As well known in the art, the speed by which a leak is detected is very important in the oil field inasmuch as the time necessary to make the test is lost and cannot be recovered in the drilling operations. Hence, time saved in conducting the test is time and money saved in drilling the well.
Another method, not used in the oil field, for checking for small leaks in pipe connections involves the use of a pressurized gas, the escape of which is sensed by a suitable sensing probe. The output of the sensing probe, which will detect minute quantities of the gas, is then displayed on a meter, screen, or the like. However, because of possible dissipation into the atmosphere by air currents, minute amounts of leakage gas could easily escape detection. A suitable enclosure has been disclosed to surround the test section and thereby prevent dissipation into the atmosphere of the test gas which leaks through the joint. An example of one form of enclosure to accomplish that purpose is shown and described in U.S. Pat. No. 4,282,743, which issued Aug. 11, 1981, to Patrick T. Pickett. However, the Pickett enclosure is not used in conjunction with an internal tool to introduce the gas and seal off the section to be tested, and the fitting arrangement disclosed in the Pickett patent is a two-piece structure which must be carefully assembled around the section to be tested and thus is too cumbersome to use in the oil field.
It is therefore desirable to provide an improved method and apparatus for pressurized testing of oil field pipe using a gas mixture that can pass through extremely small leak sites, which are too small to pass pure nitrogen gas, and which can be detected much more rapidly than pure nitrogen through leak sites that pass nitrogen but only at a slow rate.
In addition to providing an improved test gas mixture, it is also desirable that an improved leak test enclosure and pressurizing system be provided for use in conjunction with an appropriate internal pipe testing tool, wherein the pressurizing system permits pressurization of the test gas to high pressures while minimizing dangerous risks on the rig floor previously encountered and the enclosure is more convenient to use and can rapidly be applied to and removed from the pipe connection to be tested.